Hydrocarbon upgrading process

ABSTRACT

A process for recovering DCPD from a hydrocarbon feedstock comprising introducing the hydrocarbon feedstock to a first column, recovering an overhead stream from the first column comprising C 9 − hydrocarbons, recovering a bottom stream from the first column comprising C 10 + hydrocarbons, feeding the bottom stream from the first column to a second column, recovering an overhead stream from the second column comprising DCPD, and recovering a bottom stream from the second column comprising fuel oil, wherein the two columns are sized and operated at defined conditions such as pressures, temperatures, reflux rates, and reboil rates.

This application is a division of application Ser. No. 09/410,516 filedSep. 30, 1999, now U.S. Pat. No. 6,258,989.

The present invention relates to the field of hydrocarbon upgradingprocesses. More specifically, the present invention relates to theupgrading of a pyrolysis gasoline, obtained from a hydrocarbon thermalcracking process, to products such as C₅ diolefins, C₅ olefins,dicyclopentadiene, and aromatics such as benzene, toluene and xylene(BTX).

BACKGROUND OF THE INVENTION

It is well known in the art that processes for thermal cracking ofhydrocarbons such as ethane, propane, naphtha, and the like, produce aby-product referred to as pyrolysis gasoline or aromatic concentrate,which can be debutanized to form debutanized aromatic concentrate (DAC).This pyrolysis gasoline or DAC typically contains C₅ and heavierhydrocarbons, such as C₅ diolefins, C₅ olefins, aromatics,cyclopentadiene (CPD), and dicyclopentadiene (DCPD).

It is desirable to convert the CPD to DCPD which is a valuableindustrial chemical which can be used in the production of elastomersand unsaturated polyester resins.

Typical pyrolysis gasoline upgrading processes separate the pyrolysisgasoline into a C₅ stream containing CPD and a C₆+stream. The C₅ streamis then dimerized to form DCPD which is purified downstream. One problemwith this process is that when the pyrolysis gasoline is obtained fromstorage, wherein a portion of the CPD is converted to DCPD, theseparation of the pyrolysis gasoline into a C₅ stream and a C₆+stream,and dimerization of CPD in the C₅ stream to DCPD, will result insplitting the DCPD between the C₅ stream and the C₆+stream,necessitating the added expense of recovering DCPD from both the C₅stream and the C₆+stream.

Therefore, development of a process capable of efficiently upgrading apyrolysis gasoline, obtained either directly from a hydrocarbon thermalcracking unit or from storage, would be a significant contribution tothe art.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel process forupgrading a hydrocarbon feedstock comprising C₅ olefins, C₅ diolefins,CPD, DCPD and aromatics to produce a DCPD product and/or a C₅ diolefinproduct and/or a C₅ olefin product and/or an aromatic product.

It is yet another object of the present invention to provide a novelprocess of increased efficiency for recovering DCPD from pyrolysisgasoline.

It is still another object of the present invention to provide a novelprocess of increased efficiency for producing and recovering DCPD frompyrolysis gasoline containing a significant quantity of DCPD.

It is yet another object of the present invention to provide a novelprocess of increased efficiency for recovering DCPD from pyrolysisgasoline wherein the DCPD has a Pt/Co color number below about 30.

In accordance with a first embodiment of the present invention, aprocess for upgrading hydrocarbons is provided including the steps of:

a) heating a hydrocarbon feedstock comprising CPD, DCPD, C₅ diolefins,benzene, toluene, and xylene in a heating zone, to dimerize CPD to DCPD,thereby forming a first effluent;

b) separating the first effluent into a C₆+stream and a C₅ diolefinstream comprising C₅ diolefins;

c) separating the C₆+stream into a C₆-C₉ stream and a C₆+stream;

d) separating the C₁₀+stream into a fuel oil stream and a DCPD streamcomprising DCPD; and

e) hydrotreating the C₆-C₉ stream to thereby form a BTX streamcomprising benzene, toluene and xylene.

In accordance with a second embodiment of the present invention, aprocess for upgrading hydrocarbons is provided including the steps of:

a) heating a hydrocarbon feedstock comprising CPD, DCPD, C₅ diolefins,benzene, toluene, and xylene in a heating zone, to dimerize CPD to DCPD,thereby forming a first effluent;

b) separating the first effluent into a C₅-C₉ stream and a C₁₀+stream;

c) separating the C₁₀+stream into a fuel oil stream and a DCPD streamcomprising DCPD;

d) contacting the C₅-C₉ stream with a selective hydrogenation catalyst,in a first reaction zone and in the presence of hydrogen, to hydrogenateat least a portion of the diolefins, alkynes, and styrene contained inthe C₅-C₉ stream, thereby forming a second effluent;

e) separating the second effluent into a C₆-C₉ stream and a C₅ olefinstream comprising C₅ olefins;

f) contacting the C₆-C₉ stream with a hydrodesulfurization catalyst, ina second reaction zone and in the presence of hydrogen, to desulfurizeat least a portion of the sulfur-containing compounds contained in theC₆-C₉ stream thereby forming a BTX stream comprising benzene, tolueneand xylene.

In accordance with a third embodiment of the present invention, aprocess for recovering DCPD from a hydrocarbon feedstock is providedincluding the steps of:

a) providing a first separation column, a first overhead condenser, anda first reboiler, the first separation column defining a firstseparation zone having an upper portion, a lower portion and anintermediate portion, the intermediate portion of the first separationzone comprising at least about 50 theoretical trays;

b) providing a second separation column, a second overhead condenser,and a second reboiler, the second separtion column defining a secondseparation zone having an upper portion, a lower portion and anintermediate portion, the intermediate portion of the second separationzone comprising at least about 9 theoretical trays;

c) introducing a hydrocarbon feedstock comprising DCPD to theintermediate portion of the first separation zone;

d) allowing a first vaporous overhead stream comprising C₉-hydrocarbons,and having a pressure in the range of from about 0.5 psia to about 3.0psia and a temperature in the range of from about 160° F. to about 200°F., to pass from the upper portion of the first separation column to thefirst overhead condenser;

e) condensing at least a portion of the first vaporous overhead streamin the first overhead condenser thereby forming a first condensatehaving a temperature in the range of from about 50° F. to about 90° F.;

f) refluxing at least a portion of the first condensate from the firstoverhead condenser to the upper portion of the first separation zone;

g) allowing a first liquid bottoms stream comprising C₁₀+hydrocarbons topass from the lower portion of the first separation column to the firstreboiler;

h) reboiling at least a portion of the first liquid bottoms stream inthe first reboiler at a temperature in the range of from about 210° F.to about 250° F. thereby forming a first reboiled stream and a remainingportion of the first liquid bottoms stream;

i) introducing the first reboiled stream to the lower portion of thefirst separation zone;

j) introducing the remaining portion of the first liquid bottoms streamto the intermediate portion of the second separation zone;

k) allowing a second vaporous overhead stream comprising DCPD, andhaving a pressure in the range of from about 0.1 psia to about 2.0 psiaand a temperature in the range of from about 160° F. to about 200° F.,to pass from the upper portion of the second separation zone to thesecond overhead condenser;

l) condensing at least a portion of the second vaporous overhead streamin the second overhead condenser thereby forming a second condensatehaving a temperature in the range of from about 70° F. to about 100° F.;

m) refluxing at least a portion of the second condensate to the upperportion of the second separation zone and thereby forming a remainingportion of the second condensate;

n) allowing a second liquid bottoms stream comprising fuel oil to passfrom the lower portion of the second separation zone to the secondreboiler;

o) reboiling at least a portion of the second liquid bottoms stream inthe second reboiler at a temperature in the range of from about 190° F.to about 240° F. thereby forming a second reboiled stream;

p) introducing the second reboiled stream to the lower portion of thesecond separation zone; and

q) recovering the remaining portion of the second condensate from thesecond overhead condenser thereby forming a DCPD stream.

Other objects and advantages will become apparent from the detaileddescription and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flow diagram presenting an embodiment of thepresent invention.

FIG. 2 is a schematic flow diagram presenting another embodiment of thepresent invention.

FIG. 3 is a schematic flow diagram presenting yet another embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

The process of this invention involves the upgrading of a hydrocarbonfeedstock comprising CPD, DCPD, C₅diolefins, benzene, toluene, andxylene.

The hydrocarbon feedstock generally comprises hydrocarbons havinggreater than 4 carbon atoms per molecule. The hydrocarbon feedstock canbe a pyrolysis gasoline from a thermal hydrocarbon (such as ethane,propane and naphtha) cracking process. The hydrocarbon feedstock canalso be a pyrolysis gasoline which has been debutanized, and isgenerally referred to as DAC.

The hydrocarbon feedstock typically contains in the range of from about1.0 wt. % to about 20 wt. % CPD, more typically from about 1.0 wt. % toabout 15 wt. % CPD, and most typically from 1.5 wt. % to 10 wt. % CPD,based on the total weight of the hydrocarbon feedstock; and, typicallycontains in the range of from about 0.5 wt. % to about 50 wt. % DCPD,more typically from about 1.0 wt. % to about 40 wt. % DCPD, and mosttypically from 1.5 wt. % to 30 wt. % DCPD, based on the total weight ofthe hydrocarbon feedstock

In accordance with the first embodiment of the invention, thehydrocarbon feedstock is heated in a heating zone in such a manner as toprovide the dimerization of at least a portion of the CPD contained inthe hydrocarbon feedstock to DCPD, thereby forming a first effluent.More particularly, the heating in the heating zone is conducted at atemperature in the range of from about 100° F. to about 450° F.,preferably from about 200° F. to about 400° F.; and most preferably from200° F. to 300° F. The wt. % of CPD in the first effluent is preferablyless than about 2 wt. %, more preferably less than about 1.5 wt. %, andmost preferably less than 1 wt. %, based on the total weight of thefirst effluent.

The first effluent can then be separated, by any means, such asdistillation, into a C₆+stream comprising hydrocarbons having greaterthan 5 carbon atoms per molecule, and a C₅ diolefin stream comprising C₅diolefins, such as, but not limited to, isoprene and cis and trans 1,3pentadiene (piperylene).

The C₆+stream can be separated, by any suitable means, such asdistillation, into a C₆-C₉ stream comprising hydrocarbons having in therange of from and including 6 to and including 9 carbon atoms permolecule and into a C₁₀+stream comprising hydrocarbons having greaterthan 9 carbon atoms per molecule.

The C₆-C₉ stream typically contains sulfur in the range of from about 10to about 200 ppmw, more typically in the range of from about 10 to about100 ppmw, and most typically from 10 to 50 ppmw, based on the totalweight of the C₆-C₉ stream. The C₆-C₉ stream also typically has abromine number in the range of from about 10 to about 100, moretypically from about 10 to about 50, and most typically from 10 to 30grams of bromine/100 grams of sample. The bromine number, as referred toherein, is determined using ASTM test method D1492-96 and is anindicator of the amount of olefins contained in a hydrocarbon stream. Alow bromime number indicates low levels of olefins.

The C₁₀+stream can be separated, by any suitable means, such asdistillation, into a fuel oil stream comprising hydrocarbons havinggreater than 10 carbon atoms per molecule, and into a DCPD streamcomprising DCPD.

The C₆-C₉ stream can be hydrotreated, by any suitable means forhydrotreating hydrocarbons, to thereby form a BTX stream comprisingbenzene, toluene and xylene. More particularly, the hydrotreating can beaccomplished by contacting the C₆-C₉ stream with a hydrogenationcatalyst, in a first reaction zone and in the presence of hydrogen, tohydrogenate at least a portion of the olefins, diolefins, alkynes, andstyrene contained in the C₆-C₉ stream, thereby forming a second effluenthaving a lower bromine number than the C₆-C₉ stream.

The first reaction zone can be operated as a batch process step or,preferably, as a continuous process step. In the latter operation, asolid catalyst bed or a moving catalyst bed or a fluidized catalyst bedcan be employed. Any of these operational modes have advantages anddisadvantages, and those skilled in the art can select the one mostsuitable for a particular feed and catalyst.

The hydrogenation catalyst can be any composition effective forhydrogenating unsaturated hydrocarbons. More particularly, thehydrogenation catalyst can comprise, consist of, or consist essentiallyof a Group VIII metal selected from the group consisting of iron,cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinumand combinations of any two or more thereof. Preferably, thehydrogenation catalyst comprises palladium.

The hydrogenation in the first reaction zone is preferably carried outunder reaction conditions effective for hydrogenating unsaturatedhydrocarbons. The reaction temperature is more particularly in the rangeof from about 100° F. to about 600° F., preferably from about 150° F. toabout 400° F., and most preferably from 150° F. to 370° F. Thecontacting pressure can range from about 15 psia to about 1000 psia,preferably from about 50 psia to about 500 psia, and most preferablyfrom 150 psia to 500 psia. The WHSV can be in the range of from about0.1 hr.⁻¹ to about 40 hr.⁻¹, preferably from about 0.25 hr.⁻¹ to about20 hr.⁻¹, and most preferably from 1.0 hr.⁻¹ to 10 hr.⁻¹. The hydrogento hydrocarbon ratio can be in the range of from about 10 to about 5000standard cubic feet of hydrogen per barrel of hydrocarbon, preferablyfrom about 20 to about 2500, and most preferably from 100 to 1000.

The second effluent can be contacted with a hydrodesulfurizationcatalyst, in a second reaction zone and in the presence of hydrogen, todesulfurize at least a portion of the sulfur-containing compoundscontained in the second effluent, and to saturate substantially most ofthe olefinic and diolefinic compounds contained in the second effluent,thereby forming the BTX stream. The BTX stream preferably contains lessthan about 2 ppmw, more preferably less than about 1.5 ppmw, and mostpreferably less than 1.0 ppmw sulfur, based on the total weight of theBTX stream. The BTX stream also preferably has a bromine number in therange of from about 0 to about 2, preferably from about 0 to about 1,and most preferably from 0 to 0.5.

The second reaction zone can be operated as a batch process step or,preferably, as a continuous process step. In the latter operation, asolid catalyst bed or a moving catalyst bed or a fluidized catalyst bedcan be employed Any of these operational modes have advantages anddisadvantages, and those skilled in the art can select the one mostsuitable for a particular feed and catalyst.

The hydrodesulfurization catalyst can be any composition effective fordesulfurizing sulfur containing hydrocarbon feedstocks. Moreparticularly, the hydrodesulfurization catalyst can comprise, consistof, or consist essentially of a Group VIII metal selected from the groupconsisting of iron, cobalt, nickel, ruthenium rhodium, palladium,osmium, iridium, platinum, and combinations of any two or more thereof,and a Group VIB metal selected from the group consisting of chromium,molybdenum, tungsten, and combinations of any two or more thereof.Preferably, the hydrodesulfurization catalyst comprises nickel andmolybdenum.

The hydrodesulfurization in the second reaction zone is preferablycarried out under reaction conditions effective for reducing the sulfurcontent of sulfur-containing hydrocarbons and effective for saturatingolefinic hydrocarbons. The reaction temperature is more particularly inthe range of from about 300° F. to about 800° F.; preferably from about400° F. to about 700° F.; and most preferably from 500° F. to 650° F.The contacting pressure can range from about 15 psia to about 1000 psia,preferably from about 50 psia to about 500 psia, and most preferablyfrom 150 psia to 500 psia The WHSV can be in the range of from about 0.1hr.⁻¹ to about 40 hr.⁻¹, preferably from about 0.25 hr.⁻¹ to about 20hr.⁻¹, and most preferably from 1.0 hr.⁻¹ to 10 hr.⁻¹. The hydrogen tohydrocarbon ratio can be in the range of from about 10 to about 5000standard cubic feet of hydrogen per barrel of hydrocarbon, preferablyfrom about 20 to about 2500, and most preferably from 100 to 1000.

In accordance with the second embodiment of the invention, thehydrocarbon feedstock, as described above, is heated in a heating zonein such a manner as to provide the dimerization of at least a portion ofthe CPD contained in the hydrocarbon feedstock to DCPD, thereby forminga first effluent. More particularly, the heating in the heating zone isconducted at a temperature in the range of from about 100° F. to about450° F., preferably from about 200° F. to about 400° F., and mostpreferably from about 200° F. to 300° F. The wt. % of CPD in the firsteffluent is preferably less than about 2 wt. %, more preferably lessthan about 1.5 wt. %, and most preferably less than 1 wt. %, based onthe total weight of the first effluent.

The first effluent can then be separated, by any means, such asdistillation, into a C₁₀+stream comprising hydrocarbons having greaterthan 9 carbon atoms per molecule, and a C₅-C₉ stream comprisinghydrocarbons having in the range of from and including 5 to andincluding 9 carbon atoms per molecule.

The C₅-C₉ stream typically contains sulfur in the range of from about 10ppmw to about 200 ppmw, more typically from about 10 ppmw to 100 ppmw,and most typically from 10 to 50 ppmw, based on the total weight of theC₅-C₉ stream. The C₅-C₉ stream also typically has a bromine number inthe range of from about 10 to about 200, more typically from about 10 toabout 100, and most typically from 10 to 60.

The C₁₀+stream can be separated, by any suitable means, such asdistillation, into a fuel oil stream comprising hydrocarbons havinggreater than 10 carbon atoms per molecule, and into a DCPD stream.

The C₅-C₅ stream can be contacted with a selective hydrogenationcatalyst, in a first reaction zone and in the presence of hydrogen, tohydrogenate at least a portion of the diolefins, alkynes, and styrenecontained in the C₅-C₉ stream, thereby forming a second effluent havinga lower bromine number than the C₅-C₉ stream.

The first reaction zone can be operated as a batch process step or,preferably, as a continuous process step. In the latter operation, asolid catalyst bed or a moving catalyst bed or a fluidized catalyst bedcan be employed. Any of these operational modes have advantages anddisadvantages, and those skilled in the art can select the one mostsuitable for a particular feed and catalyst.

The selective hydrogenation catalyst can be any composition effectivefor selectively hydrogenating C₅ diolefins to C₅ olefins. Moreparticularly, the selective hydrogenation catalyst can comprise, consistof, or consist essentially of a first component comprising apalladium-containing material selected from the group consisting ofpalladium metal, palladium oxides, and combinations of any two or morethereof; and a second component selected from the group consisting ofsilver, or an alkali-metal halide. When the second component is silver,the catalyst can be further promoted with an alkali-metal fluoride.Suitable selective hydrogenation catalysts, and methods of making such,are disclosed in U.S. Pat. No. 5,866,735, and in U.S. Pat. No.5,510,550, which are each incorporated herein by reference. Preferably,the selective hydrogenation catalyst comprises palladium, silver andpotassium fluoride or palladium and potassium iodide. Alkali-metal, asused herein, includes lithium, sodium, potassium, rubidium, cesium andfrancium.

The hydrogenation in the first reaction zone is preferably carried outunder reaction conditions effective for hydrogenating unsaturatedhydrocarbons. The reaction temperature is more particularly in the rangeof from about 100° F. to about 600° F., preferably from about 150° F. toabout 400° F., and most preferably from 150° F. to 370° F. Thecontacting pressure can range from about 15 psia to about 1000 psia,preferably from about 50 psia to about 500 psia, and most preferablyfrom 150 psia to 500 psia. The WHSV can be in the range of from about0.1 hr.⁻¹ to about 40 hr.⁻¹, preferably from about 0.25 hr.⁻¹ to about20 hr.⁻¹, and most preferably from 1.0 hr.⁻¹ to 10 hr.⁻¹. The hydrogento hydrocarbon ratio can be in the range of from about 10 to about 5000standard cubic feet of hydrogen per barrel of hydrocarbon, preferablyfrom about 20 to about 2500, and most preferably from 100 to 1000.

The second effluent can be separated, by any suitable means, such asdistillation, into a C₆-C₉ stream comprising hydrocarbons having in therange of from and including 6 to and including 9 carbon atoms permolecule and into a C₅ olefin stream comprising C₅ olefins.

The C₆-C₉ stream can be contacted with a hydrodesulfurization catalyst,as described in the first embodiment, in a second reaction zone and inthe presence of hydrogen, to desulfurize at least a portion of thesulfur-containing compounds contained in the C₆-C₉ stream, and tosaturate substantially most of the olefinic and diolefinic compoundscontained in the C₆-C₉ stream, thereby forming a BTX stream comprisingbenzene, toluene and xylene. The BTX stream preferably contains lessthan about 2 ppmw, more preferably less than about 1.5 ppmw, and mostpreferably less than 1.0 ppmw sulfur, based on the total weight of theBTX stream. The BTX stream also preferably has a bromine number in therange of from about 0 to about 2, more preferably from about 0 to about1, and most preferably from 0 to 0.5.

The second reaction zone can be operated as a batch process step or,preferably, as a continuous process step. In the latter operation, asolid catalyst bed or a moving catalyst bed or a fluidized catalyst bedcan be employed. Any of these operational modes have advantages anddisadvantages, and those skilled in the art can select the one mostsuitable for a particular feed and catalyst.

The hydrodesulfurization in the second reaction zone is preferablycarried out under reaction conditions effective for reducing the sulfurcontent of sulfur-containing hydrocarbons and effective for saturatingolefinic hydrocarbons. The reaction temperature is more particularly inthe range of from about 300° F. to about 800° F.; preferably from about400° F. to about 700° F.; and most preferably from 500° F. to 650° F.The contacting pressure can range from about 15 psia to about 1000 psia,preferably from about 50 psia to about 500 psia, and most preferablyfrom 150 psia to 500 psia. The WHSV can be in the range of from about0.1 hr.⁻¹ to about 40 hr.⁻¹, preferably from about 0.25 hr.⁻¹ to about20 hr.⁻¹, and most preferably from 1 hr.⁻¹ to 10 hr⁻¹. The hydrogen tohydrocarbon ratio can be in the range of from about 10 to about 5000standard cubic feet of hydrogen per barrel of hydrocarbon, preferablyfrom about 20 to about 2500, and most preferably from 100 to 1000.

In accordance with the third embodiment of the invention, DCPD can berecovered from a hydrocarbon feedstock comprising DCPD. The hydrocarbonfeedstock can be the C₆+stream from the first embodiment, or the firsteffluent from the second embodiment, or any hydrocarbon streamcomprising DCPD including, but not limited to, pyrolysis gasoline asdescribed above.

A first separation column, a first overhead condenser, and a firstreboiler are provided. The fist separation column defines a firstseparation zone having an upper portion, a lower portion, and anintermediate portion. The intermediate portion of the first separationzone comprises at least about 50 theoretical trays, preferably at leastabout 55 theoretical trays, and most preferably at least 60 theoreticaltrays.

A second separation column, a second overhead condenser, and a secondreboiler arc provided. The second separation column defines a secondseparation zone having an upper portion, a lower portion, and anintermediate portion. The intermediate portion of the second separationzone comprises at least about 9 theoretical trays, preferably at leastabout 10 theoretical trays, and most preferably at least 11 theoreticaltrays.

The hydrocarbon feedstock can be introduced to the intermediate portionof the first separation zone. The theoretical tray location where thehydrocarbon feedstock is introduced to the intermediate portion of thefirst separation zone can be in the range of from about 10 to about 30,preferably from about 10 to about 20, and most preferably from 15 to 20.A first vaporous overhead stream comprising C₉−hydrocarbons(hydrocarbons having less than 10 carbon atoms per molecule), and havinga pressure in the range of from about 0.5 psia to about 3.0 psia,preferably from about 0.5 psia to about 2.0 psia, and most preferablyfrom 1.0 psia to 1.5 psia and a temperature in the range of from about160° F. to about 200° F., preferably from about 170° F. to about 200°F., and most preferably from 180° F. to 200° F., is allowed to pass fromthe upper portion of the first separation column to the first overheadcondenser wherein at least a portion of the first vaporous overheadstream is condensed, thereby forming a first condensate. The firstcondensate has a temperature in the range of forming about 50° F. toabout 90° F., more preferably from about 50° F. to about 80° F., andmost preferably from 50° F. to 70° F.

At least a portion of the first condensate can be refluxed to the upperportion of the first separation zone at a reflux ratio in the range offrom about 0.1 to about 1.0, preferably from about 0.2 to about 0.7, andmost preferably from 0.3 to 0.5. Reflux ratio, as used herein, refers tothe volume of condensate returned to the upper portion of a separationcolumn divided by the remaining volume of condensate which is notreturned to the separation column. The remaining portion of the firstcondensate (which is not refluxed) can be passed downstream for furtherprocessing. The remaining portion of the first condensate represents theC₆-C₉ stream in the first embodiment or the C₅-C₉ stream in the secondembodiment.

A first liquid bottoms stream comprising C₁₀+hydrocarbons is allowed topass from the lower portion of the first separation column to the firstreboiler wherein at least a portion of the first liquid bottoms streamis reboiled, thereby forming a first reboiled stream, at a temperaturein the range of from about 210° F. to about 250° F., preferably fromabout 210° F. to about 240° F., and most preferably from 220° F. to 230°F.

The first reboiled stream can be introduced to the lower portion of thefirst separation zone. The remaining portion of the first liquid bottomsstream, which represents the C₁₀+stream in both the first and secondembodiments, can be introduced to the intermediate portion of the secondseparation zone. The theoretical tray location where the remainingportion of the first liquid bottoms stream is introduced to theintermediate portion of the second separation zone can be in the rangeof from about 2 to about 8, preferably from about 3 to about 7, and mostpreferably from 4 to 6.

A second vaporous overhead stream comprising DCPD, and having a pressurein the range of from about 0.1 psia to about 2.0 psia, preferably fromabout 0.2 psia to about 1.0 psia, and most preferably from 0.3 psia to0.6 psia and a temperature in the range of from about 1 60° F. to about200° F., preferably from about 1 80° F. to about 200° F., and mostpreferably from 190° F. to 200° F., is allowed to pass from the upperportion of the second separation column to the second overhead condenserwherein at least a portion of the second vaporous overhead stream iscondensed, thereby forming a second condensate. The second condensatehas a temperature in the range of from about 70° F. to about 100° F.,preferably from about 80° F. to about 100° F., and more preferably from90° F. to 100° F.

At least a portion of the second condensate can be refluxed to the upperportion of the second separation zone at a reflux ratio in the range offrom about 0.1 to about 1.0, preferably from about 0.2 to about 0.7, andmost preferably from 0.3 to 0.5. The remaining portion of the secondcondensate (which is not refluxed) can be passed downstream for furtherprocessing. The remaining portion of the second condensate representsthe dicyclopentadiene stream in both the first and second embodiments.

A second liquid bottoms stream comprising fuel oil is allowed to passfrom the lower portion of the second separation column to the secondreboiler wherein at least a portion of the second liquid bottoms streamis reboiled, thereby forming a second reboiled stream, at a temperaturein the range of from about 190° F. to about 240° F., preferably fromabout 190° F. to about 220° F., and most preferably from 190° F. to 210°F.

The second reboiled stream can be introduced to the lower portion of thesecond separation zone. The remaining portion of the second liquidbottoms stream represents the fuel oil stream in both the first andsecond embodiments.

The DCPD stream produced in the first, second, or third embodiment cancomprise at least about 70 wt. % DCPD, preferably at least about 75 wt.% DCPD, and most preferably at least 80 wt. % DCPD, based on the totalweight of the DCPD stream, and has a Pt-Co color which is less thanabout 30, preferably less than about 28, and most preferably less than25. Pt-Co color, as used herein, is defined as the color of the liquidmeasured according to ASTM method D-1209.

In order to avoid the production of color bodies from the reaction ofDCPD, and other hydrocarbon compounds, with oxygen or rust, the firstseparation column, first overhead condenser, first reboiler, secondseparation column, second overhead condenser, and second reboiler mustbe operated in the substantial absence of rust and oxygen. Moreparticularly, it is preferred to operate the first separation column,first overhead condenser, first reboiler, second separation column,second overhead condenser, and second reboiler, and any ancillaryequipment, in an air tight mode. Also, it is preferred to clean, eitherchemically or otherwise, the first separation column, first overheadcondenser, first reboiler, second separation column, second overheadcondenser, second reboiler, and any ancillary equipment, prior to theiruse in the inventive process to remove substantially all of the rustcontained therein.

The following example is provided to further illustrate this inventionand is not to be considered as unduly limiting the scope of thisinvention.

EXAMPLE

This example illustrates the upgrading of a pyrolysis gasoline streamusing the inventive process as described above in the first and thirdembodiments.

A pyrolysis gasoline stream from a storage tank at a chemical plant wascharged to a heating zone (a dimerizer) at an inlet temperature of about246° F., and an outlet temperature of about 271° F., thereby forming afirst effluent. The first effluent was then separated into a C₅ diolefinstream and a C₆+stream in a first separation column (depentanizer). TheC₆+stream was then charged to a second separation column having a lowerportion, an upper portion, and an intermediate portion containingstructured packing, the intermediate portion having 58 theoreticaltrays. The point of introduction of the first effluent to theintermediate portion was at about the fifteenth theoretical tray. Thefirst vaporous overhead stream in the upper portion of the secondseparation column was at a pressure of about 1.2 psia, and a temperatureof 189° F. The overhead condenser for the second separation columncondensed the first vaporous overhead stream to yield a condensateliquid with a temperature of about 55° F., and provided a reflux streamat a reflux ratio of about 0.30. The reboiler for the second separationcolumn was operated at a temperature of about 227° F. A C₆-C₉ stream wasremoved from the condenser for the second separation column and aC₁₀+stream was removed from the reboiler for the second separationcolumn. The C₁₀+stream was then charged to a third separation columnhaving a lower portion, an upper portion, and an intermediate portioncontaining structured packing, the intermediate portion having 9theoretical trays. The point of introduction of the C₁₀+stream to theintermediate portion was at about the sixth theoretical tray. The secondvaporous overhead stream in the upper portion of the third separationcolumn was at a pressure of about 1.6 psia, and a temperature of 189° F.The overhead condenser for the third separation column condensed thesecond vaporous overhead stream to yield a condensate liquid with atemperature of about 94° F., and provided a reflux stream with a refluxratio of about 0.44. The reboiler for the third separation column wasoperated at a temperature of about 198.5° F. A DCPD stream was removedfrom the condenser for the third separation column and a fuel oil streamwas removed from the reboiler for the third separation column.

The C₆-C₉ stream from the second separation column was combined with aprefractionated raw gasoline stream (prefrac gasoline) to form acombined stream, and the combined stream was contacted with ahydrogenation catalyst containing 0.75 wt. % palladium (obtained fromEngelhard Corporation, Iselin, N.J. under product designation E347), inthe presence of hydrogen, at a pressure of about 375 psia, in a reactorwith an inlet temperature of about 166° F. The temperature differentialacross the reactor is controlled by recycling a portion of the effluentof the reactor, which has been cooled by a heat exchanger, to the middleportion of the reactor. The recycle rate is adjusted to maintain anoutlet temperature of about 270° F. The partially hydrogenated combinedstream at the outlet of the reactor constitutes a second effluent. Thesecond effluent was contacted with a hydrodesulfurization catalystcomprising nickel and molybdenum (obtained from Akzo Nobel NV, Arnhem,NL under product designation KF840), in the presence of hydrogen, at apressure of about 345 psia, an inlet temperature of about 550° F., andan outlet temperature of about 610° F., thereby producing a BTX stream.Compositional analyses of the pyrolysis gasoline stream, first effluent,C₅ diolefin stream, C₆-C₉ stream, prefrac gasoline, DCPD stream,combined stream, second effluent, and BTX stream, as analyzed by gaschromatography and normalized to sum to 100 wt. % or 100 Iv %, arepresented in the table.

TABLE Pyrol. First C₈ diolefin C₆-C₉ Prefrac. DCPD Combined Second BTXgas. stream effluent stream stream gas. stream stream effluent streamComponent wt. % wt. % wt. % wt. % wt. % wt. % lv %⁵ lv %⁵ lv %⁵Butadiene (BD)  0.37  0.35  2.16 — — — — — — C₃'s¹  0.20  0.19  1.25 — —— — — — CPD  3.70  0.86  5.15  0.10 —  0.18 — — — C₃'s²  14.07  13.85 89.25⁶ —  2.86 —  2.93¹¹  2.46¹¹  1.33¹¹ Benzene  46.18  45.58 —  79.68 39.63 —  65.17  64.90  63.96 Toluene  3.23  3.21 —  5.65  24.87 —  9.38 9.35  9.09 Styrene  0.96  0.36 —  1.77  13.08 —  4.83  0.06 — C₆-C₉ ³ 4.52⁷  4.52⁷  2.16  10.63  15.59⁹  0.02  10.97  14.65  17.29 DCPD 17.75  20.20  0.03  1.84 —  83.72 — — — C₁₀+⁴  9.02⁷  10.88⁷ —  0.33 3.97¹⁰  16.08  6.72¹⁰  8.58¹⁰  8.33¹⁰ Total 100.00 100.00 100.00 100.00100.00 100.00 100.00 100.00 100.00 Pt/Co Color 100+⁷ 100+⁷ ND 100+⁷ ND 21 ND ND ND Bromine number¹² ND⁸ ND ND ND ND ND  28.4  10.9  0.58 TotalSulfur, ppm wt. ND ND ND ND ND ND  58.9 ND  0.3 ¹- excluding BD; ²-excluding CPD; ³- excluding benzene, toluene and styrene; ⁴- excludingCDPD; ⁵- IV % = liquid volume %; ⁶- breakdown of C₃'s in C₃ diolefinstream: pentanes and cyclopentane = 1.80 wt. %; pentenes = 38.80 wt. %;isoprene = 15.55 wt. %; piperylene = 28.99 wt. %; other C₃ diolefins =4.07 wt. %; overall total C₃ diolefins = 87.41 wt. %; ⁷- estimated; ⁸-ND = not determined; ⁹- includes C₆-C₉ hydrocarbons excluding benzene,toluene and styrene; ¹⁰- includes C₉+ hydrocarbons; ¹¹- includes C₉ andlighter hydrocarbons; ¹²- Grams of Br/100 grams of sample.

From the data in the Table, it is readily apparent that the process forupgrading a hydrocarbon feedstock comprising C₅ olefins, C₅ diolefins,CPD, DCPD and aromatics (BTX) results in the production of a purifiedDCPD stream (83.72 wt. % DCPD), a purified C₅ diolefin stream (87.41wt.% C₅ diolefins), and a purified BTX stream (73.05 Iv % benzene andtoluene).

Also, the DCPD stream produced by the inventive process has a Pt/Cocolor number of 21 which is well below 30, the typical specification forDCPD product streams.

Furthermore, the total sulfur of the BTX stream was 99.5% lower than thetotal sulfur of the combined stream, and, the bromine number of the BTXstream was 98.0% lower than the bromine number of the combined stream,indicating a much lower olefin concentration in the BTX stream.

Reasonable variations, modifications, and adaptations can be made withinthe scope of the disclosure and the appended claims without departingfrom the scope of this invention.

That which is claimed is:
 1. A process for recovering DCPD from ahydrocarbon feedstock comprising the steps of: a) providing a firstseparation column, a first overhead condenser, and a first reboiler,said first separation column defining a first separation zone having anupper portion, a lower portion and an intermediate portion, saidintermediate portion of said first separation zone comprising at leastabout 50 theoretical trays; b) providing a second separation column, asecond overhead condenser, and a second reboiler, said second separationcolumn defining a second separation zone having an upper portion, alower portion and an intermediate portion, said intermediate portion ofsaid second separation zone comprising at least about 9 theoreticaltrays; c) introducing a hydrocarbon feedstock comprising DCPD to saidintermediate portion of said first separation zone; d) allowing a firstvaporous overhead stream comprising C₉−hydrocarbons, and having apressure in the range of from about 0.5 psia to about 3.0 psia and atemperature in the range of from about 160° F. to about 200° F., to passfrom said upper portion of said first separation column to said firstoverhead condenser; e) condensing at least a portion of said firstvaporous overhead stream in said first overhead condenser therebyforming a first condensate which has a temperature in the range of fromabout 50° F. to about 90° F.; f) refluxing at least a portion of saidfirst condensate from said first overhead condenser to said upperportion of said first separation zone; g) allowing a first liquidbottoms stream comprising C₁₀+hydrocarbons to pass from said lowerportion of said first separation column to said first reboiler; h)reboiling at least a portion of said first liquid bottoms stream in saidfirst reboiler at a temperature in the range of from about 210° F. toabout 250° F. thereby forming a first reboiled stream and a remainingportion of said first liquid bottoms stream; i) introducing said firstreboiled stream to said lower portion of said first separation zone; j)introducing the remaining portion of said first liquid bottoms stream tosaid intermediate portion of said second separation zone; k) allowing asecond vaporous overhead stream comprising DCPD, and having a pressurein the range of from about 0.1 psia to about 2.0 psia and a temperaturein the range of from about 160° F. to about 200° F., to pass from saidupper portion of said second separation zone to said second overheadcondenser; l) condensing at least a portion of said second vaporousoverhead stream in said second overhead condenser thereby forming asecond condensate which has a temperature in the range of from about 80°F. to about 100° F.; m) refluxing at least a portion of said secondcondensate to said upper portion of said second separation zone andthereby forming a remaining portion of said second condensate; n)allowing a second liquid bottoms stream comprising fuel oil to pass fromsaid lower portion of said second separation zone to said secondreboiler; o) reboiling at least a portion of said second liquid bottomsstream in said second reboiler at a temperature in the range of fromabout 190° F. to about 240° F. thereby forming a second reboiled stream;p) introducing said second reboiled stream to said lower portion of saidsecond separation zone; and q) recovering the remaining portion of saidsecond condensate from said second overhead condenser thereby forming aDCPD stream.
 2. A process in accordance with claim 1 wherein saidintermediate portion of said first separation zone comprises at leastabout 55 theoretical trays, said pressure of said first vaporousoverhead stream in step d) is in the range of from about 0.5 psia toabout 2.0 psia, said temperature of said first vaporous overhead streamin step d) is in the range of from about 170° F. to about 200° F., saidtemperature in step h) is in the range of from about 210° F. to about240° F., said intermediate portion of said second separation zonecomprises at least about 10 theoretical trays, said pressure of saidsecond vaporous overhead stream in step k) is in the range of from about0.2 psia to about 1.0 psia, said temperature of said second vaporousoverhead stream in step k) is in the range of from about 180° F. toabout 200° F., and said temperature in step o) is in the range of fromabout 200° F. to about 220° F.
 3. A process in accordance with claim 1wherein said intermediate portion of said first separation zonecomprises at least 60 theoretical trays, said pressure of said firstvaporous overhead stream in step d) is in the range of from 1.0 psia to1.5 psia, said temperature of said first vaporous overhead stream instep d) is in the range of from 180° F. to 200° F., said temperature instep h) is in the range of from 220° F. to 230° F., said intermediateportion of said second separation zone comprises at least 11 theoreticaltrays, said pressure of said second vaporous overhead stream in step k)is in the range of from 0.3 psia to 0.6 psia, said temperature of saidsecond vaporous overhead stream in step k) is in the range of from 190°F. to 200° F., and said temperature in step o) is in the range of from200° F. to 210° F.
 4. A process in accordance with claim 1 wherein saidhydrocarbon feedstock stream is introduced to said intermediate portionof said first separation zone at a theoretical tray location in therange of from about 10 to about
 30. 5. A process in accordance withclaim 1 wherein said hydrocarbon feedstock is introduced to saidintermediate portion of said first separation zone at a theoretical traylocation in the range of from about 10 to about
 20. 6. A process inaccordance with claim 1 wherein said hydrocarbon feedstock is introducedto said intermediate portion of said first separation zone at atheoretical tray location in the range of from 15 to
 20. 7. A process inaccordance with claim 1 wherein said remaining portion of said firstliquid bottoms stream is introduced to said intermediate portion of saidsecond separation zone at a theoretical tray location in the range offrom about 2 to about
 8. 8. A process in accordance with claim 1 whereinsaid remaining portion of said first liquid bottoms stream is introducedto said intermediate portion of said second separation zone at atheoretical tray location in the range of from about 3 to about
 7. 9. Aprocess in accordance with claim 1 wherein said remaining portion ofsaid first liquid bottoms stream is introduced to said intermediateportion of said second separation zone at a theoretical tray location inthe range of from 4 to
 6. 10. A process in accordance with claim 1wherein said at least a portion of said first condensate in step f) isrefluxed to said upper portion of said first separation zone at a refluxratio in the range of from about 0.1 to about 1.0.
 11. A process inaccordance with claim 1 wherein said at least a portion of said firstcondensate in step f) is refluxed to said upper portion of said firstseparation zone at a reflux ratio in the range of from about 0.2 toabout 0.7.
 12. A process in accordance with claim 1 wherein said atleast a portion of said first condensate in step f) is refluxed to saidupper portion of said first separation zone at a reflux ratio in therange of from 0.3 to 0.5.
 13. A process in accordance with claim 1wherein said at least a portion of said second condensate in step m) isrefluxed to said upper portion of said second separation zone at areflux ratio in the range of from about 0.1 to about 1.0.
 14. A processin accordance with claim 1 wherein said at least a portion of saidsecond condensate in step m) is refluxed to said upper portion of saidsecond separation zone at a reflux ratio in the range of from about 0.2to about 0.7.
 15. A process in accordance with claim 1 wherein said atleast a portion of said second condensate in step m) is refluxed to saidupper portion of said second separation zone at a reflux ratio in therange of from 0.3 to 0.5.
 16. A process in accordance with claim 1wherein said first separation column, said first overhead condenser,said first reboiler, said second separation column, said second overheadcondenser, and said second reboiler are operated in the substantialabsence of rust and oxygen.
 17. A process in accordance with claim 1wherein substantially all of the rust contained in said first separationcolumn, said first overhead condenser, said first reboiler, said secondseparation column, said second overhead condenser, and said secondreboiler is removed prior to step c).